Capillarity

CONTENT

• Definition of Capillarity
• Cohesion and adhesion
• Application of capillarity

Capillarity is defined as the tendency of liquids to rise or fall in narrow capillary tubes.

Cohesive force is the force of attraction between molecules of the same substance

Adhesive force is the force of attraction between molecules of different substance or it refers to the force which makes molecules of different substance to attract.

APPLICATION OF CAPILLARITY

Adhesion of water to glass is stronger than the cohesion of water, hence, when water is spilled on a clean glass surface, it wets the glass. The cohesion of mercury is greater than its adhesion to glass, hence, mercury spilled 0n glass forms small spherical droplets.

EVALUATION

1. Differentiate between cohesion and adhesion
2. Explain the rise of water in a glass capillary tube using kinetic theory

READING ASSIGNMENT

Read more on capillarity – New school physics (pg104-105)

GENERAL REVISION

1. A metal rod of length 40.0cm at 20⁰C is heated to a temperature of 45⁰C. If the new length of the rod is 40.05cm, calculate its linear expansivity.
   1. State two (2) disadvantages of thermal expansion of solids.

WEEKEND ASSIGNMENT

1. The blade of a wooden hoe feels cold to the touch in the morning than the wooden handle because the (a) blade is a better conductor of heat than the handle  (b) handle is a better conductor of heat than the blade (c) blade is placed at a lower temperature than handle (d)  handle contains store energy in the form of heat
2. Which of the following statement is not correct? (a) a sea breeze is due to convection in air  (b) cotton material are better than woollen ones for use in the same weather

(c) convection current plays an important role in the cooling of the engine of  car (d) the vacuum space in the flask helps to reduce heat loss by radiation.

3. The inside of a vacuum flask is always coated with silver to reduce heat loss by

(a) convection  (b) conduction (c)  radiation (d) evaporation

4. Which of the following colours of surface will radiate heat energy best? (a) red 

(b) white  (c) black  (d) yellow

• A hot metal in a vacuum can lose heat by (a) conduction (b) convection (c) radiation

(d) conduction and convection

THEORY

1. Differentiate between cohesion and adhesion
2. Explain the rise of water in a glass capillary tube using kinetic theory